Electrical characterization of vacuum plasma sprayed polycrystalline silicon.

摘要

Development in thin film growth techniques and understanding of transport phenomenon in polycrystalline semiconductors, has led to the development of active electronic devices using polycrystalline semiconductors, especially made of polycrystalline silicon. This dissertation is mainly concerned with understanding electrical transport in polycrystalline silicon made by Vacuum Plasma Spray, a high throughput process for making polycrystalline coatings. The essential question we ask ourselves is "Can we make an electronic device that uses plasma sprayed polycrystalline silicon as the active layer?". This general question was broken into three basic questions that have been answered to varying degrees of success. (1) What is the crystal structure, typical grain size and microstructure of VPS silicon? How do these change upon post deposition heat treatments? X-ray diffraction, Scanning Electron Microscopy and Transmission Electron Microscopy experiments have been employed to answer this question. Grain growth is shown to happen through the resolution of Cu Kalpha doublet for annealed samples. SEM and TEM micrographs show the laminar microstructure that is common for plasma sprayed coatings. (2) Does plasma sprayed polycrystaline silicon show semi-conducting behavior? If so does it retain the conductivity of the original source from which the powders were made? What is the nature of electrical conduction mechanism in VPS silicon? VPS silicon does show semi-conducting behavior and has the same type of conductivity as the starting material. Temperature dependent conductivity measurements show the presence of two activation energy for charge transport in operation in two different temperature ranges. (3) Can a model device be made using VPS silicon which can help in understanding intrinsic nature of VPS silicon and also offer possibilities for device applications? VPS polycrystalline silicon---single crystal silicon junction has been made and the nature of current transport across this interface elucidated.; A critical evaluation of the plasma spray process is presented vis-a-vis the electronic properties of polycrystalline silicon and suggestions for improvement are presented.